The field of the invention relates to refrigeration and more particularly to magnetic refrigeration utilizing wheel-type apparatus. Related to the instant invention is an invention disclosed in U.S. patent application Ser. No. 228,836, filed Jan. 27, 1981, now U.S. Pat. No. 4,332,135, which is directed to reciprocating refrigeration apparatus.
The attractiveness of the use of liquid hydrogen as a portable fuel is decreased by the cost and energy inefficiency of conventional liquefaction processes. Were these factors to be substantially reduced, liquid hydrogen would very likely be the fuel of choice to replace fossil-based fuels in many applications, and especially in the near term as jet engine aircraft fuel. The invention herein provides for the liquefying of cryogens, and hydrogen in particular, with efficiencies at least twice those of conventional liquefiers. Magnetic refrigeration carried out in accordance with the invention is based on the dependence of the entropy of certain materials on magnetic field and temperature, i.e., the magnetocaloric effect.
The invention utilizes the concept of active magnetic refrigeration in which a thermal wavefront is propagated back and forth through a regenerator during a magnetic cycle. The regenerator, composed of one or a plurality of layers of porous ferromagnetic materials, with Curie temperatures near the operating temperatures in the regenerator, should be capable of spanning large temperature differences. Several magnetic cycles such as Carnot, Brayton, or Stirling can be used. The preferred embodiment disclosed herein utilizes a Brayton cycle. The operation of such a refrigerator requires a fluid to couple the porous magnetic solid to the heat source and heat sink. Ser. No. 228,836 describes a reciprocating apparatus utilizing the concept of active magnetic regeneration.
Existing 60-W gas/cycle liquefiers, e.g., Claude cycle, operate at about 10% of Carnot efficiency. An apparatus in accordance with the present invention may operate in a range of about 60 to 90% Carnot for a 20-K to 300-K liquefier with about a 60-W cooling power operated at 20 K. A key reason for the substantial increase in efficiency from magnetic refrigerators in accordance with the invention is the elimination of room-temperature compressors and expanders which are typically present in conventional systems. Thus, a magnetic refrigeration system in accordance with the invention will not require components that produce large losses. Significantly, a magnetic refrigeration system in accordance with the invention will be less costly to construct and operate than a conventional system of the same capacity.